1. Field of the Invention
The invention relates to a method and device for estimating motion vectors, and to a video display apparatus comprising such a device.
2. Description of the Related Art
EP-B-0,410,826 [1] discloses a method of performing a recursive motion estimation between a reference image and a current image, to realize a fixed number of iterations, each iteration consisting of:
sampling both images with a resolution which increases at each iteration; PA1 detecting characteristic samples in the reference image; PA1 estimating a local motion vector for each characteristic sample in the reference image, in which the estimation is initialized with a displacement vector derived from a global motion estimation realized in the course of the iteration preceding the current iteration; and PA1 carrying out a global motion estimation of the current image, in which values of parameters of a model are calculated on the basis of the local motion vectors estimation in the course of the latest iteration. PA1 defining a first block of samples of the reference image, centered on the characteristic sample under consideration; PA1 defining a plurality of second blocks of samples of the current image centered on samples corresponding to the characteristic sample under consideration but shifted over a plurality of vectors to be tested, each vector to be tested being constituted by the vector sum of an initial displacement of the characteristic sample under consideration calculated from the global estimate of motion made in the course of the iteration preceding the iteration in progress, and from an additional displacement taken from a plurality of predetermined additional displacements; and PA1 selecting the vector to be tested which yields the best match between the respective second block and the first block to obtain the local motion vector.
To estimate the global motion, the values of 8 parameters a1 . . . a8 defining a motion model are calculated, in such a manner that a sample having coordinates X, Y is displaced to coordinates X', Y', where EQU X'=(a1.X+a2.Y+a3)/(a7.X+a8.Y+1) and EQU Y'=(a4.X+a5.Y+a6)/(a7.X+a8.Y+1),
the 8 parameters a1 . . . a8 being calculated by solving a system of equations with 8 unknowns which is constituted by the two relationships above, written for characteristic samples, the coordinates X', Y' being determined as a function of an estimated local motion vector for each of these samples and as a function of the coordinates X, Y of the sample under consideration.
To estimate a local motion vector for each characteristic sample of the current image, the following steps are carried out:
It thus appears that in the prior art, a plurality of iterations is carried out between the same images to obtain the final motion vectors corresponding to the highest resolution.